I only got part of this question right I only got part of th

I only got part of this question right.. Help needed! Nicotine patches are often used to help smokers quit.

Solution

Proportion 1
Probability Succuses( X1 )=39
No.Of Observed (n1)=256
a)
P1= X1/n1=0.15

Proportion 2
Probability Succuses(X2)=91
No.Of Observed (n2)=237
b)
P2= X2/n2=0.39

c)
Standard Error = Sqrt(p1(1-p1)/n1 + p2(1-p2)/n2 )
x = Mean
n = Sample Size
a = 1 - (Confidence Level/100)
Za/2 = Z-table value
CI = Confidence Interval
Margin of Error = Sqrt (0.002)
=0.0447

d)
CI = (p1 - p2) ± Z a/2 Sqrt(p1(1-p1)/n1 + p2(1-p2)/n2 )
C.I = (0.152-0.384) ±Z a/2 * Sqrt( (0.152*0.848/256) + (0.384*0.616/237) )
=(0.152-0.384) ± 1.28* Sqrt(0.002)
=-0.232-0.05,-0.232+0.05
=[-0.281,-0.182]